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Example: Configuring Remote LFA over LDP Tunnels in IS-IS Networks

This example shows how to configure remote LFA for LDP tunnels in an IS-IS network for extending backup protection.

Requirements

This example uses the following hardware and software components:

  • Six MX Series routers with IS-IS protocol and LDP enabled on the connected interfaces.

  • Junos OS Release 14.2 or later running on all devices.

Before you configure remote LFA over LDP tunnels in IS-IS networks, make sure of the following:

  • LDP is enabled on the loopback interface. Without a loopback interface, LDP targeted adjacency cannot be formed. Remote LFA cannot be configured without LDP targeted adjacency.

  • Remote LFA must allow asymmetric remote neighbor discovery, that is, it must send periodic targeted hellos to the router that initiated the remote neighbor for LDP auto targeted adjacency.

  • Link protection or node-link protection must be configured on the point of local repair (PLR).

Overview

The example includes six routers in a ring topology. Configure the IS-IS protocol on the directly connected interfaces. Device R1 is the PLR. This example verifies that Junos OS updates the routing table of Device R1 with LDP next-hop routes as the backup route.

Topology

Figure 1 shows the topology used in this example.

Figure 1: Configuring Remote LFA over LDP Tunnels in IS-IS Networks Configuring Remote LFA over LDP Tunnels in IS-IS Networks

Configuration

CLI Quick Configuration

To quickly configure this example, copy the following commands, paste them into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the commands into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

Router R1

Router R2

Router R3

Router R4

Router R5

Router R6

Configuring Device R1

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the CLI User Guide.

Note:

Repeat this procedure except Step 4 and 5 for every Juniper Networks router in the IGP domain, modifying the appropriate interface names, addresses, and any other parameters.

To configure Device R1:

  1. Configure the interfaces.

  2. Assign a loopback address to the device.

  3. Configure the IS-IS interface for level 2 and the metric value on all the interfaces, and enable link protection on the protected interface.

  4. Enable IS-IS node-link protection, which also automatically extends backup coverage to all LDP label-switched paths.

  5. Enable remote LFA backup which calculates the backup next hop using dynamic LDP label-switched path.

    (Optional) When you include the node link degradation statement even if node protection LFA is not configured for a given destination, the device uses the configured link protection LFA as the backup for the primary link.

  6. Configure MPLS to use LDP label-switched paths for all interfaces on the device.

  7. Specify a time interval for which the targeted LDP sessions are kept up when the remote LFA goes down, and specify a maximum number of automatically, targeted LDP sessions to optimize the use of memory.

  8. (Optional) Enable forwarding equivalence class (FEC) deaggregation, which results in faster global convergence.

  9. To enable Packet Forwarding Engine local repair, establish a policy that forces the routing protocol process to install all the next hops for a given route.

    This policy ensures that the backup route is installed in the forwarding table used by the Packet Forwarding Engine to forward traffic to a given destination.

  10. Apply the policy to the forwarding table of the local router with the export statement.

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

If you are done configuring the device, enter commit from the configuration mode.

Verification

Confirm that the configuration is working properly.

Verifying the Routes

Purpose

Verify that the expected routes are learned.

Action

On Device R1, from operational mode, run the show route command to display the routes in the routing table.

Meaning

The output shows all the routes in the routing table of Device R1.

Verifying the IS-IS Routes

Purpose

Display all the LDP backup routes in the IS-IS routing table of Device R1.

Action

On Device R1, from operational mode, run the show isis route command to display the routes in the IS-IS routing table.

Meaning

The output shows all the LDP backup routes in the IS-IS routing table of Device R1.

Verifying the LDP Routes

Purpose

Verify the automatically targeted LDP routes.

Action

From operational mode, enter the show ldp session auto-targeted detail command.

Meaning

The output shows automatically targeted LDP next hops.

Verifying the Designated Backup Path Node

Purpose

Display the remote LFA next hop determined for a given destination.

Action

From operational mode, enter the show isis backup spf results command.

Meaning

The output indicates whether a specific interface or node has been designated as a remote backup path and why.